1. Field of the Invention
The present invention relates to a controller for controlling a component or components of a motor vehicle such as an engine, such that a controllable variable such as a torque, speed or horsepower of the engine, an input shaft speed or speed reduction ratio of an automatic transmission of the vehicle, or a drive torque or acceleration value of the vehicle coincides with a desired or target value. More particularly, the invention is concerned with a device and a method for determining a target value of such a controllable variable associated with the running state of the vehicle.
2. Discussion of the Prior Art
In an automotive vehicle, the engine, automatic transmission and other components or units are controlled so that the actual values of controllable variables or parameters such as the horsepower, torque and speed of the engine, and the input shaft speed and speed reduction ratio of the automatic transmission are regulated so as to coincide with respective desired or target values which are determined from time to time.
For instance, Publication No. 61-8305 of examined Japanese Patent Application proposes a method of controlling a vehicle engine by regulating a throttle actuator so that the actual speed of the engine coincides with a determined target value. An alternative method of controlling the vehicle engine is disclosed in Publication No. 60-155044, wherein the throttle actuator is controlled so that the actual engine horsepower is made equal to a determined target horsepower value.
The target engine horsepower or torque, for example, is generally determined depending upon the currently detected amount of operation of the accelerator pedal, and according to a predetermined relationship between the optimum target horsepower or torque value and the operating amount of the accelerator pedal. The predetermined relationship is represented by a data map stored in the relevant controller. The target value may be determined depending upon the currently detected running speed of the vehicle as well as the operating amount of the accelerator pedal, according to a predetermined relationship among these three parameters, i.e., horsepower or torque of the engine, operating amount of the accelerator pedal and running speed of the vehicle.
For improved regulation of the running condition of the vehicle, it is desirable to use other parameters representative of the vehicle running condition such as the road surface gradient and the vehicle weight (including the load), to determine the desired or target value of the engine horsepower or torque, for example. In this case, however, the calculation of the target value requires an extremely complicated procedure. For instance, when the target engine horsepower value is calculated based on the operating amount of the accelerator pedal, the road surface gradient and the vehicle running speed and weight, the calculation requires data processing according to data map (or functional equations) involving the four independent variables and the relevant variable (target horsepower) to be controlled.
In connection with the gradient of the road surface, for example, it is possible to determine the target horsepower value, depending upon whether the gradient value is "relatively small" or "relatively large". According to this arrangement, the target horsepower value largely changes stepwise from one value to another, depending upon whether the road surface gradient is smaller or larger than a predetermined threshold value which defines the boundary between the two road gradient conditions, i.e., "inclined road" and "non-inclined road". To avoid this inconvenience, it is necessary to use an expensive sensor for more accurately detecting the road gradient, so that the determined target horsepower value more exactly reflects the actual gradient of the road on which the vehicle is running. However, this solution needs considerably complicated data map regarding the road gradient.
On the other hand, the quantitative detection of a parameter such as the road gradient or vehicle weight representing the vehicle running condition does not meet the practical requirement in controlling a controllable variable such as the engine torque or vehicle drive torque. Namely, the practical requirement is based on the qualitative analysis of the vehicle running parameter, for example, depending upon whether the gradient is relatively large or relatively small. For example, the determined target drive torque is increased by a relatively small amount if the uphill road gradient is relatively small. Thus, the quantitative detection of vehicle running parameters to determine the target value of a controllable variable is not practically necessary, and complicates the determination of the target value, where the qualitative analysis of the running parameter satisfies the practical need.